CCAR1/CoCoA pair-mediated recruitment of the Mediator defines a novel pathway for GATA1 function

ER-phagy: mechanisms, regulation and diseases connected to the lysosomal clearance of the endoplasmic reticulum

ER-phagy (reticulo-phagy) defines the degradation of portions of the endoplasmic reticulum (ER) within lysosomes or vacuoles. It is part of the self-digestion (i.e., auto-phagic) programs recycling cytoplasmic material and organelles, which rapidly mobilize metabolites in cells confronted with nutrient shortage. Moreover, selective clearance of ER subdomains participates to the control of ER size and activity during ER stress, the re-establishment of ER homeostasis after ER stress resolution and the removal of ER parts, in which aberrant and potentially cytotoxic material has been segregated. ER-phagy relies on the individual and/or concerted activation of the ER-phagy receptors, ER peripheral or integral membrane proteins that share the presence of LC3/Atg8-binding motifs in their cytosolic domains. ER-phagy involves the physical separation of portions of the ER from the bulk ER network, and their delivery to the endolysosomal/vacuolar catabolic district. This last step is accomplished by a variety of mechanisms including macro-ER-phagy (in which ER fragments are sequestered by double-membrane autophagosomes that eventually fuse with lysosomes/vacuoles), micro-ER-phagy (in which ER fragments are directly engulfed by endosomes/lysosomes/vacuoles), or direct fusion of ER-derived vesicles with lysosomes/vacuoles. ER-phagy is dysfunctional in specific human diseases and its regulators are subverted by pathogens, highlighting its crucial role for cell and organism life.

Genetic Factors Associated With Tardive Dyskinesia: From Pre-clinical Models to Clinical Studies

Tardive dyskinesia is a severe motor adverse event of antipsychotic medication, characterized by involuntary athetoid movements of the trunk, limbs, and/or orofacial areas. It affects two to ten patients under long-term administration of antipsychotics that do not subside for years even after the drug is stopped. Dopamine, serotonin, cannabinoid receptors, oxidative stress, plasticity factors, signaling cascades, as well as CYP isoenzymes and transporters have been associated with tardive dyskinesia (TD) occurrence in terms of genetic variability and metabolic capacity. Besides the factors related to the drug and the dose and patients’ clinical characteristics, a very crucial variable of TD development is individual susceptibility and genetic predisposition. This review summarizes the studies in experimental animal models and clinical studies focusing on the impact of genetic variations on TD occurrence. We identified eight genes emerging from preclinical findings that also reached statistical significance in at least one clinical study. The results of clinical studies are often conflicting and non-conclusive enough to support implementation in clinical practice.

Critical roles of transcriptional coactivator MED1 in the formation and function of mouse adipose tissues

In this study, Ito et al. sought to understand the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue. Using multiple genetic approaches to assess requirements for MED1 in adipocyte formation and function in mice, they show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy.

The MED1 subunit has been shown to mediate ligand-dependent binding of the Mediator coactivator complex to multiple nuclear receptors, including the adipogenic PPARγ, and to play an essential role in ectopic PPARγ-induced adipogenesis of mouse embryonic fibroblasts. However, the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue have been unclear. Here, after establishing requirements for MED1, including specific domains, for differentiation of 3T3L1 cells and both primary white and brown preadipocytes, we used multiple genetic approaches to assess requirements for MED1 in adipocyte formation, maintenance, and function in mice. We show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy. This work establishes MED1 as an essential transcriptional coactivator that ensures homeostatic functions of adipocytes.

PML-RARα induces all-trans retinoic acid-dependent transcriptional activation through interaction with MED1

Transcriptional activation by PML-RARα, an acute promyelocytic leukemia-related oncofusion protein, requires pharmacological concentrations of all-trans retinoic acid (ATRA). However, the mechanism by which the liganded PML-RARα complex leads to the formation of the preinitiation complex has been unidentified. Here we demonstrate that the Mediator subunit MED1 plays an important role in the ATRA-dependent activation of the PML-RARα-bound promoter. Luciferase reporter assays showed that PML-RARα induced significant transcription at pharmacological doses (1 μM) of ATRA; however, this was submaximal and equivalent to the level of transcription driven by intact RARα at physiological doses (1 nM) of ATRA. Transcription depended upon the interaction of PML-RARα with the two LxxLL nuclear receptor recognition motifs of MED1, and LxxLL→LxxAA mutations led to minimal transcription. Mechanistically, MED1 interacted ATRA-dependently with the RARα portion of PML-RARα through the two LxxLL motifs of MED1. These results suggest that PML-RARα initiates ATRA-induced transcription through its interaction with MED1.

Long noncoding RNA LINC00052 inhibits colorectal cancer metastasis by sponging microRNA-574-5p to modulate CALCOCO1 expression

The dysregulation of long-chain noncoding ribonucleic acid (lncRNA) is a common phenomenon in many human cancers. Some studies on the biological function of long intergenic non-protein-coding RNA 52 (LINC00052) in cancer indicate that this gene can act as either oncogene or tumor suppressor in some kinds of cancers, such as breast cancer, gastric cancer, liver cancer, and lung cancer. However, the biological function of LINC00052 in colorectal cancer (CRC) has not been studied. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and Western blot (WB) techniques were applied to detect the expression levels of LINC00052, miR-574-5p, and calcium-binding and coiled-coil domain 1 (CALCOCO1) in CRC cells and tissues. We authenticated the biological function of LINC00052 and miR-574-5p in CRC, and find some target genes for LINC00052 and miR-574-5p via bioinformatics methods. Dual-luciferase reporter gene assay was performed to identify the interaction between LINC00052 and miR-574-5p or CALCOCO1 and miR-574-5p. The results demonstrated that LINC00052 was downregulated in CRC tissues compared with their adjacent tissues. And LINC00052 could suppress CRC cells metastasis both in vivo and in vitro. Beyond that, miR-574-5p was upregulated in CRC tissues, and as an oncogene, it accelerated CRC cell migration and invasion. More importantly, the results of our research demonstrated that LINC00052 could regulate the expression of CALCOCO1 via sponging miR-574-5p in CRC. Overall, our study illuminated the lncRNA-miRNA functional networks in CRC, and these results might provide a new research direction for the diagnosis and treatment of CRC.

Drosophila Mediator Subunit Med1 Is Required for GATA-Dependent Developmental Processes: Divergent Binding Interfaces for Conserved Coactivator Functions

DNA-bound transcription factors (TFs) governing developmental gene regulation have been proposed to recruit polymerase II machinery at gene promoters through specific interactions with dedicated subunits of the evolutionarily conserved Mediator (MED) complex. However, whether such MED subunit-specific functions and partnerships have been conserved during evolution has been poorly investigated. To address this issue, we generated the first Drosophila melanogaster loss-of-function mutants for Med1, known as a specific cofactor for GATA TFs and hormone nuclear receptors in mammals. We show that Med1 is required for cell proliferation and hematopoietic differentiation depending on the GATA TF Serpent (Srp). Med1 physically binds Srp in cultured cells and in vitro through its conserved GATA zinc finger DNA-binding domain and the divergent Med1 C terminus. Interestingly, GATA-Srp interaction occurs through the longest Med1 isoform, suggesting a functional diversity of MED complex populations. Furthermore, we show that Med1 acts as a coactivator for the GATA factor Pannier during thoracic development. In conclusion, the Med1 requirement for GATA-dependent regulatory processes is a common feature in insects and mammals, although binding interfaces have diverged. Further work in Drosophila should bring valuable insights to fully understand GATA-MED functional partnerships, which probably involve other MED subunits depending on the cellular context.

Infection perturbs Bach2- and Bach1-dependent erythroid lineage 'choice' to cause anemia

Elucidation of how the differentiation of hematopoietic stem and progenitor cells (HSPCs) is reconfigured in response to the environment is critical for understanding the biology and disorder of hematopoiesis. Here we found that the transcription factors (TFs) Bach2 and Bach1 promoted erythropoiesis by regulating heme metabolism in committed erythroid cells to sustain erythroblast maturation and by reinforcing erythroid commitment at the erythro-myeloid bifurcation step. Bach TFs repressed expression of the gene encoding the transcription factor C/EBPβ, as well as that of its target genes encoding molecules important for myelopoiesis and inflammation; they achieved the latter by binding to their regulatory regions also bound by C/EBPβ. Lipopolysaccharide diminished the expression of Bach TFs in progenitor cells and promoted myeloid differentiation. Overexpression of Bach2 in HSPCs promoted erythroid development and inhibited myelopoiesis. Knockdown of BACH1 or BACH2 in human CD34⁺ HSPCs impaired erythroid differentiation in vitro. Thus, Bach TFs accelerate erythroid commitment by suppressing the myeloid program at steady state. Anemia of inflammation and myelodysplastic syndrome might involve reduced activity of Bach TFs.

Fetal γ-globin genes are regulated by the BGLT3 long noncoding RNA locus

Long noncoding RNAs (lncRNAs) are increasingly being appreciated as participants in regulation of important cellular processes, including transcription. Because lncRNAs are highly cell type specific, they have the potential to contribute to the unique transcriptional repertoire of diverse cells, but underlying mechanisms are unclear. We studied BGLT3, an erythroid lncRNA encoded downstream of ^Aγ-globin (HBG1). BGLT3 and γ-globin genes are dynamically cotranscribed in erythroid cells in vivo. Deletion of BGLT3 using CRISPR/Cas9 editing shows that it specifically contributes to regulation of γ-globin genes. We used reduction or overexpression of the RNA and inhibition of transcription through the locus by CRISPRi to distinguish functions of the transcript vs the underlying sequence. Transcription of the BGLT3 locus is critical for looping between the γ-globin genes and BGLT3 sequences. In contrast, the BGLT3 transcript is dispensable for γ-globin/BGLT3 looping but interacts with the mediator complex on chromatin. Manipulation of the BGLT3 locus does not compromise γ-globin gene long-range looping interactions with the β-globin locus control region (LCR). These data reveal that BGLT3 regulates γ-globin transcription in a developmental stage-specific fashion together with the LCR by serving as a separate means to increase RNA Pol II density at the γ-globin promoters.

CARP-1/CCAR1: a biphasic regulator of cancer cell growth and apoptosis

Targeted cancer therapy using small molecule inhibitors (SMIs) has been useful in targeting the tumor cells while sparing the normal cells. Despite clinical success of many targeted therapies, their off-target effects and development of resistance are emerging as significant and challenging problems. Thus, there is an urgent need to identify targets to devise new means to treat cancers and their drug-resistant phenotypes. CARP-1/CCAR1 (Cell division cycle and apoptosis regulator 1), a peri-nuclear phospho-protein, plays a dynamic role in regulating cell growth and apoptosis by serving as a co-activator of steroid/thyroid nuclear receptors, β-catenin, Anaphase Promoting Complex/Cyclosome (APC/C) E3 ligase, and tumor suppressor p53. CARP-1/CCAR1 also regulates chemotherapy-dependent apoptosis. CARP-1/CCAR1 functional mimetics (CFMs) are a novel SMIs of CARP-1/CCAR1 interaction with APC/C. CFMs promote apoptosis in a manner independent of p53. CFMs are potent inhibitors of a variety of cancer cells including the drug (Adriamycin or Tamoxifen)-resistant breast cancer cells but not the immortalized breast epithelial cells, while a nano-lipid formulation of the lead compound CFM-4 improves its bioavailability and efficacy in vivo when administered orally. This review focuses on the background and pleiotropic roles of CARP-1/CCAR1 as well as its apoptosis signaling mechanisms in response to chemotherapy in cancer cells.